1. Field of Invention
This invention relates to wireless communication and more particularly to an improved method and system for determining spurious emission output by a wireless terminal.
2. Description of Related Art
A relatively recent advance in telecommunication technology is an ability for people to use wireless terminals to communicate with others. The wireless terminal can take a variety of forms. The wireless terminal may be, for example, a cellular phone, a pager, a personal digital assistant (PDA), a portable computer with wireless modem, or a fixed wireless terminal.
A wireless network, alone or together with one or more other networks, communicatively couples the wireless terminal to a remote terminal, e.g., another cellular telephone, pager, PDA, portable computer with wireless modem, or fixed wireless terminal. The wireless network typically has a base station that produces a radiation pattern. The radiation pattern defines a coverage area of the wireless network. The wireless terminal exchanges signals with the base station within the coverage area of the wireless network. The base station, in turn, facilitates exchange of the signals with the remote terminal, thereby allowing communication between the wireless terminal and the remote terminal.
There may be signal interference present over the air interface. The signal interference is typically caused by unauthorized devices transmitting within the coverage area of the wireless network. To overcome the signal interference, the base station may adjust a transmit power setting of the wireless terminal, i.e., instruct the wireless terminal to adjust a transmit power at which the wireless terminal transmits signals. The wireless terminal may be set to transmit signals at a high transmit power given a high amount of signal interference over the air interface. In contrast, the wireless terminal may be set to transmit signals at a low transmit power given a low amount of signal interference over the air interface. As a result, the wireless terminal may transmit signals at a plurality of transmit powers settings during operation.
The signals that the wireless terminal transmits should be confined to a spread spectrum channel. The spread spectrum channel may be defined by, for instance, a range of frequencies spanning 1.25 MHz. Frequencies between 1850 MHz and 1990 MHz defines a personal communication service (PCS) band. The spread spectrum channel may be located within the PCS band, but could also be located in some other band.
Certification houses typically measure spurious emission output by a wireless terminal. Spurious emission output by the wireless terminal is any signals transmitted by the wireless terminal, outside of the spread spectrum channel which the wireless terminal is supposed to transmit signals. The spurious emission can be produced in a variety of ways. The wireless terminal can have a power amplifier. The power amplifier amplifies signals for transmission over the spread spectrum channel. In amplifying the signals for transmission, the power amplifier may add unwanted transient, high power noise to the signal. The transient, high power noise may be produced at harmonics of a carrier frequency of the spread spectrum channel, thus causing the wireless terminal to transmit signals outside of the spread spectrum channel. The signals transmitted outside of the spread spectrum signal are spurious emission output by the wireless terminal. Other reasons why a wireless terminal produces spurious emission are also possible.
Telecommunications Industry Association/Electronics Industry Association (TIA/EIA) has promulgated a standard (TIA/EIA-98) that defines a test that certification houses can use to determine the spurious emission output by a wireless terminal. TIA/EIA-98 describes instructing the wireless terminal to transmit signals, over a spread spectrum channel, at a maximum transmit power setting. Then, a determination is made as whether the wireless terminal produces any spurious emission. Certification houses that test for spurious emission output by the wireless terminal actually instruct the wireless terminal to transmit signals at the maximum transmit power setting over not one, but two or three different spread spectrum channels. Then, the certification houses measure the spurious emission output by the wireless terminal for the different spread spectrum channels. Performance of the wireless terminal is characterized in terms of the spurious emission output by the wireless terminal for the two or three different spread spectrum channels.